This invention generally relates to the testing of subscriber lines prior to cutover of a replacement switching system. The invention more specifically relates to a system capable of subscriber line verification prior to replacing a switch providing conventional wire line service with an integrated digital carrier switch.
When an existing switch is being replaced, there exists a need to verify that a new switching system has been properly wired and configured so that the telephone number assigned a subscriber served by the existing switch is still associated with that subscriber by the new switch. A wiring error or an erroneous entry in the database of the new switching system could cause a service interruption to the subscribers of the old switching system.
FIG. 1 illustrates a known approach for verification of a subscriber line when switching from an analog switch to a different analog switch. An existing analog switch 10 provides service via path 12 to a main distribution frame (MDF) 14 having internal path 16 to external wire 18 which is connected to customer premise equipment (CPE) 20 such as a conventional telephone. A new analog switch 22 is connected by path 24 and path 26 in the MDF to line 18. New switch 22 is also connected to the analog switch 10 by an office-to-office (OTO) trunk 28. A directory number in new switch 22 believed to correspond to CPE 20 is transmitted over the OTO trunk 28 to analog switch 10. Switch 10 responds by establishing a metallic connection between trunk 28 and the MDF by paths 12 and 16. New switch 22 generates a contact closure on trunk 28. The test is successfully completed if the new switch 22 detects the closure at the MDF as coupled by paths 24 and 26. Failure to detect the closure within a predetermined time indicates that a wiring error or directory problem exists. If a problem does exist, this verification test permits it to be resolved prior to switching service for CPE 20 to the new analog switch 22. After a successful test, subscriber line 18 can be cut over to be served by new switch 22 through paths 24 and 26. Path 16 is cut to complete the transfer of service.
FIG. 2 illustrates a switching system in which existing subscriber lines 34 are to be cut over from an existing wire analog system to a digital carrier facility such as the AT&T Universal SLC.RTM. System. Existing analog switch 30 is connected by MDF 32 to a plurality of analog subscriber lines 34 which serve CPE 36 and 40. Subscriber line 38 connects the CPE 40 through the MDF to analog switch 30. The digital carrier system includes a central office terminal (COT) 42 connected by a digital communication channel 44, such as a T1 channel, to a remote terminal (RT) 46. The COT is normally located in the central office and the RT is located near the telephone equipment. Analog lines 48 between the COT and the MDF correspond to each subscriber line to be supported by the digital carrier system. After cutover, the RT will be coupled by a plurality of analog lines 50 to the subscriber equipment. A channel 44 utilizes multiplexed signals to carry information being communicated over each subscriber line coupled by the RT 46 and associated command and status signals. This digital system minimizes the number of long wire lines which must be maintained. A metallic test line 52 is connected between analog switch 30 and COT 42. Metallic test line 54 couples COT 42 and RT 46. The RT includes a channel test unit (CTU) 56 and a plurality of channel units (CU) 58 which provide interfaces for the different subscriber lines to be supported.
The pre-cutover testing of subscriber line 38 which supports CPE 40 is described as follows. A path 60 in MDF 32 establishes a connection between COT 42 and subscriber line 38 at the central office. An analog line 62 which is one of lines 50 connects CPE 40 to a CU in RT 46. The analog switch 30 utilizes a conventional pair gain test controller (not shown) to establish a continuous metallic path to line 62 via path 52, COT 42, path 54, CTU 56, and a CU 58. An off-hook condition forced by the analog switch 30 on the metallic test path will be reflected back to switch 30 via line 38 if the wiring is correct. Also the forced off-hook should be reported from the CU to the RT and COT and path 48 and 60 back to the switch 30. U.S. Pat. No. 4,653,043 assigned to the same assignee as the present patent, provides a more detailed description of the utilization of the metallic paths for pre-cutover verification.
It is important to note that each channel unit normally supplies battery to the CPE 36 as connected by lines 50. However, the channel test unit may be utilized with the metallic test lines to place one of the lines 50 in a test mode wherein the battery supply is disconnected. Thus, lines 50 are installed and tested one at a time in order to avoid a service impairment problem that could arise from providing parallel battery supplies from the analog switch via lines 34 and from the channel units via lines 50. Substantial technician cutover support is required to connect and verify each of the lines to be cut over to the digital carrier service.
FIG. 3 illustrates a conversion from an analog switch utilizing a universal digital carrier system to a digital switch utilizing an integrated digital carrier system. Like reference numerals in the FIGS. denote common elements. A digital switch 64, such as an AT&T 5ESS.RTM. system, provides digital switching and an integrated digital carrier system. A multiplexed channel 66 couples switch 64 to the multiplexed channel 44 which is utilized to provide service to CPE 36. Subscriber line verification testing is accomplished using metallic contact paths 52 and 54 in combination with the reception of signal information transmitted on channel 44 that is received by digital switch 64 via channel 66. An office-to-office trunk 68 allows switch 64 to establish a test connection through analog switch 30 and utilize metallic test paths 52 and 54 to provide verification testing prior to cutover of the subscriber service. A subscriber number contained in a directory number translation database in digital switch 64 is sent over the OTO trunk to analog switch 30 which initiates a corresponding connection. Precutover verification of the subscriber number is determined by digital switch 64 by monitoring the communications from RT 46 to COT 42 via cables 44 and 66. After verification and correction, if needed, of the digital switch database, the COT 42, MDF 32, and analog switch 30 may be removed from service upon switch 64 being set to post-cutover operation. A more detailed description of the cutover and testing utilized in the system shown in FIG. 3 is provided by U.S. Pat. No. 4,653,043, which is incorporated by reference herein.
FIG. 4 illustrates the post-cutover system following the conversion illustrated in FIG. 3. Digital switch 70 utilizes a multiplexed channel 72 to provide signaling through RT 74 via analog lines 76 to CPE 78. The illustrated configuration can result from the conversion, as described in FIG. 3 or may represent a new initial installation.
The prior art has failed to provide a solution to the cutover verification of an analog switch utilizing wire subscriber lines directly to a digital switch using integrated digital carrier facilities. Although it is possible to provide an evolution utilizing a COT and an RT as an interim step, this technique is costly in that the COT is retired following conversion to the digital switch and thus, represents additional costs. Further, such a transition requires substantial technician support, especially, in the transition as shown in FIG. 2. Thus, there exists a need to provide an improved pre-cutover verification for a direct conversion from an analog switch using wire lines to a digital switch using an integrated digital carrier system and a multiplexed channel.